The present invention relates to accumulators for the absorption of shock pulses and the suppression of pressure pulses and surges in hydraulic systems and more particularly to an in-line pressure accumulator designed as an integral part of the construction of hydraulic lines interconnecting components in such systems.
Pressure pulses generated by valve closures and component operation in high pressure hydraulic systems cause shock and other high energy disturbances and oscillations (often referred to as water hammer) which can rupture lines and otherwise cause piping and component failure. Such pressure surges often cause physical movements of system piping and components and their support structures.
Accumulators to suppress such pressure surges and component movement have been known. An in-line type pressure and volume accumulator is shown in U.S. Pat. No. 2,677,393 which used a radially convoluted, elongate, self supporting cylinder made of strips of metal sheet suitably joined together to form the containment member or pipeline. But the structure was not suitable for high pressure operation and was not suitably strong or supported and contained. U.S. Pat. No. 3,665,967 proposes the use of an elastomeric stretchable inner tube supported in a closed cell foam encased in a flexible hose. Such a stretchable inner tube is, however, unreliable since its section is significantly reduced when stretched and the combination of high internal pressure and stretching through repeated cycling can cause rupture of the inner tube. Use of a bellows similar to U.S. Pat. No. 2,677,399 has been proposed in U.S. Pat. No. 4,500,487 for a one-shot energy absorber in which a longitudinal bellows is mounted in a crushable metallic foam support. Such a system is used as a safety feature in nuclear reactors to prevent a pressure surge so high so as to rupture the piping system and result in leak or discharge of radioactive coolants. However, U.S. Pat. No. 4,500,487 does not address continuously operating accumulators such as in aircraft hydraulic systems. None of these prior art proposals satisfies the need for a an accumulator for ongoing use as part of an aircraft hydraulic system requiring only occasional maintenance.
Discrete accumulators have, of course, been used to solve this and similar problems and often have been used in multiples to be inserted at predetermined locations in a fluid-flow system. However, such accumulators' primarily function is as reservoirs, are heavy, and have been designed for use at lower pressures for pump output smoothing. But, for very high pressures, 3,000 psi, an improved structure is required.